Composite Fiber Web Having Superior Heat Resistance and Sound Absorption and Method of Manufacturing Same

ABSTRACT

A composite fiber web having superior heat resistance and sound absorption and including a center layer containing a carbon fiber and a heat-resistant layer, and to a method of manufacturing the same. The method of the present invention can exhibit a fast manufacturing speed through a melt-blowing process that will generate economic benefits. The composite fiber web includes a composite layer and individual layers with various fiber diameters resulting in a superior sound absorption rate. The PET fiber included in the heat-resistant layer of the composite layer is an environmentally friendly material with superior heat resistance due to the inclusion of ultrafine fiber. Also, the composite fiber web has superior strength, conductivity, and electromagnetic shielding and deodorization effects, which allows it to be widely utilized for sound absorption materials and in all application fields thereof.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to and the benefit of Korean PatentApplication No. 10-2019-0104246, filed on Aug. 26, 2019, which isincorporated herein by reference in its entirety.

FIELD

The present disclosure relates to a composite melt-blown fiber webhaving superior heat resistance and sound absorption and including acenter layer containing a carbon fiber and a heat-resistant layer, and amethod of manufacturing the same.

BACKGROUND

The statements in this section merely provide background informationrelated to the present disclosure and may not constitute prior art.

Typically, external noise is introduced into vehicles through variouspaths during driving. Friction noise between tires and the ground, noisegenerated by high-temperature high-pressure combustion gas flow in theexhaust system, and engine transmission noise generated by engines andtransmitted through vehicle bodies or the air are all transferred to theears of persons in the vehicles, degrading the quietness withinvehicles.

To reduce engine transmission noise, an engine cover or a hood insulatoris generally used, but there are limits to removing the enginetransmission noise to a desired level.

Hence, vehicles are provided with sound absorption materials on thefront, left side and floor. For example, the sound absorption materialis attached to a dash panel that separates the engine space and thecabin space in order to block the noise generated in the engine space.The sound absorption material is also attached to a side panel in orderto block the noise introduced through the side of the vehicle body.

Examples of the sound absorption material typically include glass fiber,urethane foam, and recycled fabric felt. With respect to urethane foam,which is most commonly used, it has a foul odor and a risk of emittingtoxic gas in the event of an accident due to the inflammability thereof,and when the foam is manufactured as a sound absorption material, it isdifficult to shape.

Moreover, in recent years, national regulations associated withenvironmental friendliness and recyclability have progressively becomemore stringent, and fiber felt made from thermoplastic resins such aspolypropylene (PP), rather than urethane foam, is being widely used.However, polypropylene-resin-based sound absorption materials have weakheat resistance, and a fiber material mixed therewith also has alimitation in that the fiber itself does not have heat resistance orflame retardancy and thus does not contribute to the properties thereof.

Therefore, there is a desire for a sound absorption material that isenvironmentally friendly, has superior heat resistance and soundabsorption, and contributes to desired properties.

SUMMARY

The present disclosure provides a composite fiber web including a centerlayer containing a carbon fiber and a heat-resistant layer formed on atleast one surface of the center layer.

The present disclosure is to provide a method of manufacturing thecomposite fiber web by continuously manufacturing and stacking thecenter layer and the heat-resistant layers through a melt-blowingprocess.

The present disclosure is not limited to the foregoing, and will beclearly understood through the following description and realized by themeans described in the claims and combinations thereof.

The present disclosure provides a composite fiber web, including acenter layer containing a carbon fiber, and a heat-resistant layerformed on at least one surface of the center layer.

The composite fiber web may further include an outer layer formed on theheat-resistant layer and including a nonwoven fabric.

The composite fiber web may include 20 to 35 wt % of the center layer,51 to 69 wt % of the heat-resistant layer, and 11 to 14 wt % of theouter layer.

The heat-resistant layer may include 43 to 78 wt % of a polyethyleneterephthalate (PET) fiber and 20 to 55 wt % of a staple fiber.

The heat-resistant layer may further include 2 to 5 wt % of anantioxidant.

The PET fiber may have a fiber diameter of 2 to 12 μm, an intrinsicviscosity (IV) of 0.43 to 0.5, and a melt flow rate (MFR) of 150 to 1500g/10 min.

The staple fiber may be at least one of a hollow staple fiber, amodified cross-section hollow fiber, a modified cross-section fiber, ora cross-section fiber, and may have a thickness of 2.0 to 6.0 denier anda length of 18 to 68 mm.

The composite fiber web may have a weight of 580 to 690 g/m², athickness of 20 to 26 mm, an average fiber diameter of 2 to 15 μm, aheat-resistant temperature of 225 to 235° C., and an average noisereduction coefficient (NRC) of 0.92 to 0.94.

The present disclosure provides a method of manufacturing the compositefiber web, which includes manufacturing a center layer containing acarbon fiber, manufacturing a heat-resistant layer, forming a compositelayer by stacking the heat-resistant layer on at least one surface ofthe center layer, and stacking an outer layer on at least one surface ofthe composite layer.

Manufacturing the center layer may include extruding an isotropic pitchresin, spinning the extruded pitch resin to afford a pitch-based carbonfiber, subjecting the carbon fiber to infusibilization, carbonizing thecarbon fiber subjected to infusibilization, and treating the carbonizedcarbon fiber with water vapor.

Spinning the extruded pitch resin may be performed at a spinning nozzletemperature 50 to 70° C. higher than a softening temperature of thepitch and at a hot-air temperature 30 to 50° C. higher than thesoftening temperature of the pitch.

Subjecting the carbon fiber to infusibilization may be performed at atemperature 20 to 30° C. higher than a softening temperature of thepitch and at a belt speed of 0.3 to 1 m/min in an oxygen gas atmosphere.

Carbonizing the carbon fiber may be performed at 900 to 1100° C. in aninert gas atmosphere.

Manufacturing the heat-resistant layer may include crystallizing apolyethylene terephthalate (PET) resin, drying the crystallized PETresin, extruding the dried PET resin, spinning the extruded PET resin toprepare a PET fiber, and mixing the PET fiber with a staple fiber.

Crystallizing the PET resin may be performed at a temperature of 110 to130° C. for 3 to 6 hr to thereby crystallize a surface of the PET resin.

Drying the crystallized PET resin may be performed at a temperature of150 to 170° C. for 3 to 4 hr.

Spinning the extruded PET resin may be performed at a spinningtemperature of 200 to 300° C. and a spinning speed of 30 to 120 m/s.

Manufacturing the heat-resistant layer may further include performingheat treatment after the spinning, in which the heat treatment may beperformed by heat-treating the spun PET fiber at a heat treatmenttemperature of 50 to 100° C. and a belt speed of 0.3 to 1 m/min.

The method of manufacturing the composite fiber web may include, on acontinuously moving conveyor belt, manufacturing the heat-resistantlayer, obtained by mixing a PET fiber resulting from crystallizing,drying, extruding and spinning a PET resin with a staple fiber, into afirst web and a third web, manufacturing the center layer, obtained bysubjecting a pitch-based carbon fiber resulting from spinning anextruded pitch resin to infusibilization, carbonization and water-vaportreatment, into a second web, and stacking the first web to the thirdweb, which are continuously manufactured, in the order of firstweb/second web/third web.

The method of manufacturing a composite fiber web enables a center layerand heat-resistant layers to be continuously manufactured and stackedthrough a melt-blowing process, and the shortened manufacturing timegenerates economic benefits.

The composite fiber web also includes a composite layer and individuallayers with various fiber diameters for a superior sound absorptionrate. A polyethylene terephthalate (PET) fiber included in theheat-resistant layer of the composite layer in place of urethane is anenvironmentally friendly material, including an ultrafine fiber, thusexhibiting superior heat resistance.

Also, according to the present disclosure, not only does the compositefiber web have superior strength and conductivity, but it also haselectromagnetic shielding and deodorization effects, and can thus bewidely utilized for sound absorption materials and in all applicablefields thereof.

The effects of the present invention are not limited to the foregoing,and should be understood to include all effects that can be reasonablyanticipated from the following description.

Further areas of applicability will become apparent from the descriptionprovided herein. It should be understood that the description andspecific examples are intended for purposes of illustration only and arenot intended to limit the scope of the present disclosure.

DRAWINGS

To better understand the disclosure, various forms will now bedescribed, given by way of example, reference being made to theaccompanying drawings, in which:

FIG. 1 is a cross-sectional view schematically showing a composite fiberweb according to the present invention;

FIG. 2 is a flowchart showing a process of manufacturing a compositefiber web according to the present disclosure;

FIG. 3A is a microscope image showing the center layer according to thepresent disclosure;

FIG. 3B is microscope images showing the heat-resistant layer accordingto the present disclosure;

FIG. 4 shows a vertical melt-blown manufacturing apparatus according tothe present disclosure, by which the first web to the third web arecontinuously stacked in the order of first web/second web/third web;

FIG. 5 is a graph showing the sound absorption coefficient depending onthe frequency of Example 1 according to the present disclosure and theComparative Example;

FIG. 6 is a graph showing the sound absorption coefficient depending onthe frequency of Example 2 and Example 3 according to the presentdisclosure; and

FIG. 7 is a graph showing the sound absorption coefficient depending onthe frequency of Example 1 and Examples 4 and 5 according to the presentdisclosure.

The drawings described herein are for illustration purposes only and arenot intended to limit the scope of the present disclosure in any way.

DETAILED DESCRIPTION

The features and advantages of the present disclosure will be moreclearly understood from the following forms taken in conjunction withthe accompanying drawings. The present disclosure is not limited to theforms disclosed herein, and may be modified into different forms. Theseforms are provided to thoroughly explain the present disclosure and tosufficiently transfer the spirit of the present disclosure to thoseskilled in the art. It should be understood that throughout thedrawings, corresponding reference numerals indicate like orcorresponding parts and features.

Throughout the drawings, the same reference numerals will refer to thesame or like elements. It will be understood that, although terms suchas “first” and “second” may be used herein to describe various elements,these elements are not to be limited by these terms. These terms areonly used to distinguish one element from another element. For instance,a “first” element discussed below could be termed a “second” elementwithout departing from the scope of the present disclosure. Similarly,the “second” element could also be termed a “first” element. As usedherein, the singular forms are intended to include the plural forms aswell, unless the context clearly indicates otherwise.

It will be further understood that the terms “comprise”, “include”,“have”, etc., when used in this specification, specify the presence ofstated features, integers, steps, operations, elements, components, orcombinations thereof, but do not preclude the presence or addition ofone or more other features, integers, steps, operations, elements,components, or combinations thereof. Also, it will be understood thatwhen an element such as a layer, film, area, or sheet is referred to asbeing “on” another element, it can be directly on the other element, orintervening elements may be present therebetween. Similarly, when anelement such as a layer, film, area, or sheet is referred to as being“under” another element, it can be directly under the other element, orintervening elements may be present therebetween.

Unless otherwise specified, all numbers, values, and/or representationsthat express the amounts of components, reaction conditions, polymercompositions, and mixtures used herein are to be taken as approximationsincluding various uncertainties affecting the measurements thatessentially occur in obtaining these values, among others, and thusshould be understood to be modified by the term “about” in all cases.Furthermore, when a numerical range is disclosed in this specification,the range is continuous, and includes all values from the minimum valueof said range to the maximum value thereof, unless otherwise indicated.Moreover, when such a range pertains to integer values, all integersincluding the minimum value to the maximum value are included, unlessotherwise indicated.

FIG. 1 is a cross-sectional view schematically showing a composite fiberweb 1 according to one form of the present disclosure. With referencethereto, the composite fiber web 1 includes a center layer 10 containingcarbon fiber and a heat-resistant layer 20 formed on at least onesurface of the center layer 10. Also, the composite fiber web 1 mayfurther include a nonwoven fabric layer 30 formed on the heat-resistantlayer 20.

In one form of the present disclosure, the composite fiber web includes20 to 35 wt % of the center layer, 51 to 69 wt % of the heat-resistantlayer, and 11 to 14 wt % of the outer layer.

The amount of each component of the composite fiber web, which will bedescribed below, is represented based on 100 wt % of the composite fiberweb. If the amount basis thereof is changed, the new basis will alwaysbe set forth so that a person skilled in the art will clearly know thebasis on which the amount is described.

Composite Fiber Web

(1) Center Layer

In the composite fiber web 1 according one form of the presentdisclosure, the center layer 10 is not particularly limited, so long asit contains a carbon fiber.

The center layer of the present disclosure may include a carbon fiberobtained by spinning an anisotropic pitch or an isotropic pitch, andpreferably a carbon fiber obtained by spinning an isotropic pitch, whichhas higher strength and thus superior durability.

According to the present disclosure, the amount of the center layer maybe 20 to 35 wt % based on the total weight of the composite fiber web.If the amount thereof is less than 20 wt %, heat resistance maydecrease. On the other hand, if the amount thereof exceeds 35 wt %,rigidity may decrease.

In the present disclosure, the thickness ratio of the center layer andthe heat-resistant layer may be 1:1 to 1:4, for example, 1:1, 1:2 or1:4, and particularly, the composite layer may include a heat-resistantlayer/a center layer/a heat-resistant layer at a thickness ratio of1:2:1, 1:1:1 or 2:1:2. If the thickness ratio is less than 1:1, rigiditymay decrease. On the other hand, if the thickness ratio exceeds 1:4,heat resistance may decrease.

(2) Heat-Resistant Layer

The heat-resistant layer 20 according to an embodiment of the presentdisclosure is not particularly limited, so long as it is able toincrease the heat resistance of the composite fiber web according to thepresent disclosure.

According to the present disclosure, the heat-resistant layer may beformed on at least one surface of the center layer 10 of the presentdisclosure, and particularly on the upper surface and the lower surfaceof the center layer.

The heat-resistant layer of the present disclosure may include materialssuch as a polyester fiber in order to increase heat resistance, andparticularly a polyethylene terephthalate (PET) fiber, which hassuperior heat resistance and is environmentally friendly. The PET fiberaccording to the present disclosure may have a fiber diameter of 2 to 12μm, an intrinsic viscosity (IV) of 0.43 to 0.5, and a melt flow rate(MFR) of 150 to 1500 g/10 min. If the amount of the fiber having adiameter less than 2 μm is 50% or more, the heat resistance maydecrease. On the other hand, if the amount of the fiber having adiameter greater than 12 μm is 50% or more, the sound absorption ratemay decrease. Also, if the intrinsic viscosity is less than 0.43, heatresistance may decrease. On the other hand, if the intrinsic viscosityexceeds 0.5, sound absorption may decrease. Also, if the melt flow rateis less than 150 g/10 min or exceeds 1500 g/10 min, heat resistance andsound absorption may decrease.

The heat-resistant layer according to the present disclosure may alsoinclude a staple fiber in order to increase the sound absorption rateand strength at low frequencies. The staple fiber according to thepresent disclosure may be at least one of a hollow staple fiber, amodified cross-section hollow fiber, a modified cross-section fiber, ora cross-section fiber, and preferably is a modified cross-section hollowfiber. According to the present disclosure, the staple fiber has athickness of 2.0 to 6.0 denier, preferably 3.0 to 5.0 denier, and alength of 18 to 68 mm. If the thickness thereof is less than 2.0 denier,heat insulation properties may decrease. On the other hand, if thethickness thereof exceeds 6.0 denier, the staple fiber may not beuniformly distributed in the PET fiber. Also, if the length thereof isless than 18 mm, the staple fiber may not be uniformly distributed inthe heat-resistant layer. On the other hand, if the length thereofexceeds 68 mm, staple fiber agglomeration may occur.

Also, the heat-resistant layer according to the present disclosure mayfurther include an antioxidant in order to increase heat resistance. Theantioxidant of the present disclosure may be a phenol-based antioxidant,an amine-based antioxidant, a sulfur-based antioxidant, aphosphorus-based antioxidant, and the like, and a phenol-basedantioxidant is particularly useful as a primary antioxidant thatincreases heat resistance by suppressing oxidation by inhibiting adouble chain reaction.

The heat-resistant layer according to the present disclosure may include43 to 78 wt % of the PET fiber, 20 to 55 wt % of the staple fiber, and 2to 5 wt % of the antioxidant. If the amount of the PET fiber is lessthan 43 wt %, the strength and sound absorption of the fiber web maydecrease. On the other hand, if the amount thereof exceeds 78 wt %, thethickness, bulkiness, and restoring capability may decrease, undesirablydeteriorating sound absorption. Also, if the amount of the staple fiberis less than 20 wt %, bulkiness and restoring capability may decrease,undesirably deteriorating sound absorption. On the other hand, if theamount thereof exceeds 55 wt %, the strength and sound absorption of thecomposite fiber web may decrease. Also, if the amount of the antioxidantis less than 2 wt %, heat resistance may decrease. On the other hand, ifthe amount thereof exceeds 5 wt %, sound absorption may decrease.

The amount of the heat-resistant layer according to the presentdisclosure may be 51 to 69 wt % based on the total weight of thecomposite fiber web. If the amount thereof is less than 51 wt % orexceeds 69 wt %, heat resistance and sound absorption may decrease.

The thickness of the heat-resistant layer according to the presentdisclosure is the same as described in connection with the center layerabove.

(3) Outer Layer

The outer layer 30 according to an embodiment of the present disclosureis not particularly limited, so long as it has heat resistance andself-extinguishing properties.

The outer layer according to the present disclosure may include anonwoven fabric, and examples of the nonwoven fabric may include a PETspunbond nonwoven fabric, a PET needle-punched nonwoven fabric, and achemical nonwoven fabric, and preferably useful as a flame-retardantchemical nonwoven fabric is a PET chemical nonwoven fabric.

The amount of the outer layer according to the present disclosure may be11 to 14 wt %. If the amount thereof is less than 11 wt % or exceeds 14wt %, heat resistance and sound absorption may decrease.

(4) Composite Fiber Web

The composite fiber web manufactured according to one form of thepresent disclosure has a weight of 580 to 690 g/m², a thickness of 20 to30 mm, a fiber diameter of 2 to 15 μm and a specific surface area of 900to 2,500 m²/g. If the weight thereof is less than 580 g/m², soundabsorption may decrease, whereas if the weight thereof exceeds 690 g/m²,the thickness thereof may increase and thus processability may decrease.Also, if the thickness thereof is less than 20 mm, sound absorption maydecrease, whereas if the thickness thereof exceeds 30 mm, processabilitymay decrease. Also, if the fiber diameter thereof is less than 2 μm,heat resistance may decrease, whereas if the fiber diameter thereofexceeds 15 μm, sound absorption may decrease. Also, if the specificsurface area thereof is less than 900 m²/g, adsorption and deodorizationperformance may decrease, whereas if the specific surface area thereofexceeds 2,500 m²/g, rigidity may decrease.

Specifically, the composite fiber web according to the presentdisclosure is configured to include the center layer and theheat-resistant layer at a predetermined ratio and having predetermineddiameters, in which the heat-resistant layer includes the PET fiber andthe staple fiber, having predetermined diameters, at a predeterminedratio. The composite fiber web has a heat-resistant temperature of 225to 235° C. and an average noise reduction coefficient (NRC) of 0.92 to0.94, thus exhibiting superior heat resistance (a heat-resistanttemperature of 80° C. or more) and sound absorption (NRC of 0.1 or more)compared to bases for use in conventional sound absorption materials.The composite fiber web having a specific ratio according to the presentdisclosure has not only heat resistance and sound absorption but alsohigh durability and conductivity, and may thus be widely utilized forsound absorption materials and in all application fields thereof.

FIG. 2 is a flowchart showing the process of manufacturing the compositefiber web 1 according to the present disclosure. With reference thereto,the method of the present disclosure includes manufacturing a centerlayer containing a carbon fiber (S10), manufacturing a heat-resistantlayer containing a polyester fiber (S20), forming a composite layer bystacking the heat-resistant layer on at least one surface of the centerlayer (S30) and stacking an outer layer on at least one surface of thecomposite layer (S40).

Manufacturing the center layer (S10), as shown in FIG. 3A, involvesmanufacturing a center layer containing a carbon fiber. Specifically,manufacturing the center layer includes extruding an isotropic pitchresin, spinning the extruded pitch resin to afford a pitch-based carbonfiber, subjecting the carbon fiber to infusibilization, carbonizing thecarbon fiber subjected to infusibilization, and treating the carbonizedcarbon fiber with water vapor.

The material for the carbon fiber included in the center layer accordingto the present disclosure is preferably an isotropic pitch resin, whichhas a high modulus value to thus exhibit high rigidity, no thermaldeformation even at high temperatures, and ability to be manufactured tohave the desired properties depending on the manufacturing method. Theisotropic pitch resin according to the present disclosure may beobtained from coal tar and petroleum residue oil.

The isotropic pitch resin prepared above is extruded and spun to obtaina pitch-based carbon fiber. In the present disclosure, the pitch resinis spun through a melt-blown spinning process to form a thin fiber usingtraction at the point of contact with the polymer melt discharged fromthe spinning nozzle by jetting high-speed hot air to the air nozzles ofknife edges facing each other at a predetermined angle. The pitch usedin the present disclosure may have a softening temperature of 190 to210° C., and thus the spinning process may be performed at a nozzletemperature 50 to 70° C. higher than the softening temperature of thepitch and at a hot-air temperature 30 to 50° C. higher than thesoftening temperature of the pitch. If the nozzle temperature is lessthan 50° C. higher than the softening temperature of the isotropicpitch, the pitch may not melt due to the low temperature. On the otherhand, if the nozzle temperature is more than 70° C. higher than thesoftening temperature of the isotropic pitch, it is difficult to performa spinning process due to carbonization. Also, if the hot-airtemperature is less than 30° C. or more than 50° C. higher than thesoftening temperature of the isotropic pitch, a drawing process may notproceed properly upon pitch spinning.

Next, the pitch-based carbon fiber thus spun and manufactured issubjected to infusibilization. Specifically, the spun carbon fiber isstacked in the form of a sheet through a melt-blowing collector and thensubjected to infusibilization. In the present disclosure,infusibilization is intended to impart thermal stability to the carbonfiber before carbonization of the carbon fiber, in which oxygenmolecules diffuse/move toward the core of fiber strands and thusfunction as a crosslinker, thereby enhancing both the physical strengthand the thermal stability of the spun carbon fiber. Accordingly, thecarbon fiber is subjected to infusibilization at a temperature 20 to 30°C. higher than the softening temperature of the pitch and a belt speedof 0.3 to 1 m/min in an oxygen gas atmosphere. If the above processingtemperature is less than 20° C. or more than 30° C. higher than thesoftening temperature of the pitch, infusibilization may not occur,undesirably deteriorating physical strength and thermal stability.Moreover, since the carbon fiber included in the center layer ismanufactured on a continuously moving conveyor belt, if the belt speedis less than 0.3 m/min or exceeds 1 m/min, infusibilization may notproceed properly.

Next, the carbon fiber subjected to infusibilization is carbonized. Inthe present disclosure, the carbonization process enables hetero atoms(H, N, O, S, and the like) to be removed from the pitch-based material.Thus, the carbon fiber subjected to infusibilization may be carbonizedat a temperature of 900 to 1100° C. for 30 sec to 5 min in an inert gasatmosphere. Here, if the processing temperature is lower than 900° C. orhigher than 1100° C., the carbonization process may not proceedefficiently. Also, if the processing time is shorter than 30 sec orlonger than 5 min, the carbonization process may not proceedefficiently.

Finally, the carbonized carbon fiber may be treated with water vapor. Inthe present disclosure, water-vapor treatment enables surfaceactivation, and additionally, in order to increase adsorption propertiesbefore and after the carbonization of the carbon fiber, the carbon fibermay be activated by the addition of oxidative gas or reactive orchemical material to form pores. Here, the carbon fiber may be activatedby adjusting the draw ratio in the range of 1.0 to 5.0, and the specificsurface area of the activated carbon fiber may be 900 to 2,500 m²/g.

Manufacturing the heat-resistant layer (S20) as shown in FIG. 3Binvolves manufacturing the heat-resistant layer containing a polyesterfiber. Specifically, crystallizing a polyethylene terephthalate (PET)resin, drying the crystallized PET resin, extruding the dried PET resin,spinning the extruded PET resin to afford a PET fiber, and mixing thePET fiber with a staple fiber are performed.

Crystallizing the PET resin involves pre-crystallizing the surface ofthe PET resin in order to inhibit PET resin chips from sticking togetherand agglomerating when the PET resin is rapidly introduced at a hightemperature for extrusion and spinning. According to the presentdisclosure, the surface of the PET resin may be crystallized at atemperature of 110 to 130° C. for 3 to 6 hr. If the crystallizationtemperature is lower than 110° C., crystallization does not occur andsticking may take place upon spinning. On the other hand, if thetemperature is higher than 130° C., spinning may not occur due tocarbonization, discoloration and sticking. Also, if the crystallizationtime is shorter than 3 hr, crystallization does not occur, whereas ifthe time exceeds 6 hr, spinning may not occur due to carbonization,discoloration and sticking.

The crystallized PET resin is dried in order to inhibit the molecularweight of the PET resin from decreasing due to hydrolysis by water inthe air before extruding and spinning the PET resin and to make themolecular weight difference between PET resin chips uniform. Accordingto the present disclosure, the PET resin may be dried at 150 to 170° C.for 3 to 4 hr, whereby the water content in the PET resin may becontrolled to 50 ppm or less. If the water content exceeds 50 ppm, thedrawing process does not proceed properly due to the molecular weightdifference during spinning, or the spinning process may not occurefficiently. If the drying temperature is lower than 150° C., the dryingprocess does not proceed properly and thus the water content may become50 ppm or more, whereas if the drying temperature is higher than 170°C., carbonization, discoloration and sticking may occur due to the hightemperature, making it impossible to perform the spinning process. Also,if the drying time is less than 3 hr, the water content may be 50 ppm ormore, and thus the spinning process may not occur efficiently.

The dried PET resin is extruded and spun to obtain a PET microfiber. Inthe present disclosure, the PET resin may be spun at a spinningtemperature of 200 to 300° C. and a spinning speed of 30 to 120 m/s. Ifthe spinning temperature is lower than 200° C., the drawing process maynot proceed properly, undesirably deteriorating heat resistance andsound absorption. On the other hand, if the spinning temperature ishigher than 300° C., the nozzle may become clogged due to carbonizationinside the extruder. Also, if the spinning speed is less than 30 m/s orexceeds 120 m/s, the drawing process may not proceed properly,undesirably deteriorating heat resistance and sound absorption.Moreover, heat treatment may be further performed after the spinningprocess according to the present disclosure. The heat treatment processis capable of improving the thermal stability of the PET fiber bypassing the spun PET fiber through a stabilization furnace to heat-treatthe surface thereof. The spun PET fiber may be heat-treated at atemperature of 80 to 120° C. and a belt speed of 0.3 to 1 m/min. If theheat treatment temperature is lower than 80° C., heat treatment may notproceed properly, undesirably deteriorating heat resistance. On theother hand, if the heat treatment temperature is higher than 120° C.,the fiber may break down due to the high temperature, undesirablydeteriorating the sound absorption rate and rigidity. Also, if the beltspeed is less than 0.3 m/min or exceeds 1 m/m in, heat treatment may notproceed properly, undesirably deteriorating heat resistance and soundabsorption.

The PET fiber thus spun and heat-treated with the staple fiber may bemixed with the staple fiber in order to supplement the insufficientperformance of the PET fiber, namely the strength thereof and the soundabsorption rate thereof at a low frequency. In the present disclosure,the fiber-mixing process may be carried out through air carding or airblowing. The content of the staple fiber mixed therewith is the same asdescribed above.

Forming the composite layer (S30) may be performed by stacking theheat-resistant layer on at least one surface of the center layer.Preferably, the composite layer is configured such that theheat-resistant layer is stacked on the upper and lower surfaces of thecenter layer. In forming the composite layer according to the presentdisclosure, as shown in FIG. 4, the center layer and the heat-resistantlayers are sequentially spun and stacked on respective conveyor beltsthrough at least three melt-blown spinning T-dies (nozzles) using avertical melt-blown manufacturing apparatus. Specifically, forming thecomposite layer includes, on the continuously moving conveyor belt ofthe vertical melt-blown manufacturing apparatus, manufacturing theheat-resistant layer, obtained by mixing the PET fiber resulting fromcrystallizing, drying, extruding and spinning the PET resin with thestaple fiber, into a first web and a third web; manufacturing the centerlayer, obtained by subjecting the pitch-based carbon fiber resultingfrom spinning the extruded pitch resin to stacking, infusibilization,carbonization and water-vapor treatment, into a second web; and stackingthe first web to the third web, which are continuously manufactured, inthe order of first web/second web/third web. According to the presentdisclosure, the method of manufacturing the composite fiber web iscapable of continuously manufacturing and stacking the center layer andthe heat-resistant layers using a melt-blowing process, thus exhibitinga fast manufacturing speed and generating economic benefits.

Stacking the outer layer (S40) involves stacking the outer layer on atleast one surface of the composite layer. This step is performed tofurther increase heat resistance by stacking the outer layer on theupper and lower surfaces of the composite layer manufactured through themelt-blowing process. This stacking process is a typical technique thatmay be used in the art of the present disclosure, and is notparticularly limited, so long as the outer layer may be stacked. Thecomponents for the stacked outer layer are the same as those describedfor the outer layer above.

A better understanding of the present disclosure will be given throughthe following examples, which are merely set forth to illustrate thepresent disclosure but are not to be construed as limiting the scope ofthe present disclosure.

Example 1

(S10) 20 kg of an isotropic pitch resin was prepared from coal tar andpetroleum residue oil. Thereafter, the isotropic pitch resin wasextruded and spun. Here, the softening temperature of the isotropicpitch resin was 200° C., and thus the isotropic pitch resin was spun ata nozzle temperature of 260° C. and a hot-air temperature of 240° C.,thereby obtaining a pitch-based carbon fiber. Thereafter, thepitch-based carbon fiber was subjected to infusibilization at atemperature of 230° C. and a belt speed of 0.9 m/min in an oxygen gasatmosphere. Thereafter, the carbon fiber subjected to infusibilizationwas carbonized at 1,000° C. for 1 to 2 min in an inert gas (nitrogengas) atmosphere to remove impurities. Finally, the carbonized carbonfiber was activated with water-vapor treatment to manufacture a centerlayer including a carbon fiber web of 200 g/m².

(S20) 500 kg of a polyethylene terephthalate (PET) resin having a fiberdiameter of 10 μm, an intrinsic viscosity (IV) of 0.43 and a melt flowrate of 250 g/10 min was prepared and treated at 130° C. for 5 hr tocrystallize the surface of the PET resin. Thereafter, the crystallizedPET resin was dried at 160° C. for 4 hr to thus inhibit hydrolysisthereof. Thereafter, the dried PET resin was extruded and spun at atemperature of 280° C. and a spinning speed of 50 m/s to obtain a PETfiber. The PET fiber was subjected to surface heat treatment for thermalstabilization at a heat treatment temperature of 90° C. and a belt speedof 0.9 m/min using a thermal stabilization furnace. Thereafter, as aPET-based modified cross-section hollow fiber, a staple fiber having athickness of 4 denier and a length of 38 mm was prepared, and 35 wt % ofthe staple fiber was mixed with 65 wt % of the heat-treated PET fiber tomanufacture a heat-resistant layer including a PET melt-blown fiber webof 200 g/m².

(S30) On the continuously moving conveyor belt of a vertical melt-blownmanufacturing apparatus, the heat-resistant layer obtained in S20 wasmanufactured into a first web and a third web. Also, the center layerobtained in S10 was manufactured into a second web. Thereafter, takingeither the first web or the third web, which were continuouslymanufactured, a composite layer was manufactured by stacking in theorder of first web/second web/third web at a thickness ratio of 1:1:1.

(S40) The upper and lower surfaces of the composite layer were laminatedwith a chemical nonwoven fabric of 40 g/m², thereby manufacturing acomposite fiber web in which the center layer accounted for 29.4 wt %thereof, the two heat-resistant layers accounted for 58.8 wt % thereof,and the outer layers accounted for 11.8 wt % thereof, and having a totalweight of 680 g/m², an average fiber diameter (a carbon fiber web and aPET melt-blown fiber web) of 2 to 15 μm and a thickness of 25 mm.

Example 2

A composite fiber web in which a center layer accounted for 34.5 wt %thereof, two heat-resistant layers accounted for 51.7 wt % thereof, andouter layers accounted for 13.8 wt % thereof, and having a total weightof 580 g/m² and a thickness of 20 mm was manufactured in the same manneras in Example 1, with the exception of the heat-resistant layerincluding a PET melt-blown fiber web of 150 g/m².

Example 3

A composite fiber web in which a center layer accounted for 20.5 wt %thereof, two heat-resistant layers accounted for 68.5 wt % thereof andouter layers accounted for 11 wt % thereof, and having a total weight of730 g/m² and a thickness of 22 mm was manufactured in the same manner asin Example 1, with the exception of the center layer including a carbonfiber web of 150 g/m² and the heat-resistant layer including a PETmelt-blown fiber web of 250 g/m².

Example 4

A composite fiber web having a total weight of 690 g/m², an averagefiber diameter (a carbon fiber web and a PET melt-blown fiber web) of 3to 15 μm and a thickness of 26 mm was manufactured in the same manner asin Example 1, with the exception of having a PET fiber obtained using aPET resin having an intrinsic viscosity (IV) of 0.46 was applied.

Example 5

A composite fiber web having a total weight of 685 g/m², an averagefiber diameter (a carbon fiber web and a PET melt-blown fiber web) of 3to 15 μm and a thickness of 25 mm was manufactured in the same manner asin Example 1, with the exception of having a PET fiber obtained using aPET resin having an intrinsic viscosity (IV) of 0.50 was applied.

Comparative Example

A PET fiber web having a total weight of 700 g/m², a thickness of 22 mmand an average fiber diameter of 3 to 10 μm was manufactured from afiber obtained by melt-spinning a typical PET fiber.

Test Example 1—Evaluation of Average Fiber Diameter and Superior SoundAbsorption and Heat Resistance

The composite fiber web of Example 1 and the PET fiber web of theComparative Example were compared for the average fiber diameter, soundabsorption and heat resistance.

In Test Example 1, the fiber diameter was measured in accordance with KSK ISO 1973 in a manner in which the weight of the conditioned fiber wasmeasured, the line density was calculated, an electron microscope imagewas obtained, and the diameters of 20 or more samples were measured andaveraged.

In Test Example 1, heat resistance was evaluated by measuring themaximum temperature at which there were no changes in color and outerappearance after 24 hr from 130° C. and elevating the temperature by 10°C. to thus determine the maximum temperature.

In Test Example 1, sound absorption was evaluated in a manner in which atest sample having a size of 1 m×1.2 m was placed in a chamber, 15 soundsources from 400 Hz to 10,000 Hz were input and the sound absorptionrate of the material for reverberation thereof was measured.

The results of measuring the weight, thickness and average fiberdiameter of Example 1 and the Comparative Example are shown in Table 1below.

TABLE 1 No. Example 1 Comparative Example Construction PET fiber web +carbon PET fiber web fiber web + PET fiber web Weight (g/m²) 680 700Thickness (mm)  25  22 Average fiber 2 to 15 3 to 10 diameter (μm)

The results of measuring the heat resistance and sound absorption ofExample 1 and Comparative Example are shown in Tables 2 and 3,respectively.

TABLE 2 No. Example 1 Comparative Example Maximum temperature at which230° C. 150° C. heat resistance is maintained

TABLE 3 (FREQ [Hz]) 500 630 800 1k 1.25k 1.6k 2k 2.5k 3.15k 4k 5k 6.3k8k 10k Example 1 0.55 0.72 0.88 0.95 0.98 0.99 1.02 1.08 1.03 1.05 1.051.06 1.04 1.07 Comparative 0.43 0.61 0.80 0.90 0.92 0.95 1.00 1.02 0.980.99 0.99 1.00 1.00 1.02 Example

As is apparent from Table 1, the composite fiber web of Example 1 of thepresent disclosure was slightly thicker (by 3 mm) than that of theComparative Example, but the average fiber diameter was thinner and theweight was less. When the composite fiber web of the present disclosureis used as a sound absorption material for vehicles and the like, it canbe confirmed that it is advantageous with respect to fuel efficiency. Asis apparent from Table 2, the heat-resistant temperature of Example 1was determined to be 230° C., which is 80° C. higher than that of theComparative Example.

With reference to Table 3 and FIG. 5, the sound absorption coefficientat each frequency was higher in Example 1 than in the ComparativeExample.

Therefore, compared to the monolayered PET fiber web, the compositefiber web according to the present disclosure was configured to includethe composite layer with individual layers having various fiberdiameters, thereby exhibiting a superior sound absorption rate andhigher heat resistance by virtue of the materials of the individuallayers.

Test Example 2—Measurement of Sound Absorption Performance Depending onWeight Ratio of Center Layer and Heat-Resistant Layer

The composite fiber web of Example 1 and the composite fiber webs ofExamples 2 and 3 were compared for sound absorption. The soundabsorption in Test Example 2 was tested in the same manner as in TestExample 1.

The results of sound absorption testing of Example 1 and Examples 2 and3 are shown in Table 4 below and FIG. 6.

TABLE 4 (FREQ [Hz]) 500 630 800 1k 1.25k 1.6k 2k 2.5k 3.15k 4k 5k 6.3k8k 10k Example 2 0.50 0.68 0.86 0.91 0.98 0.99 1.02 1.02 1.02 1.00 1.001.02 1.05 1.00 Example 3 0.53 0.70 0.88 0.94 0.99 0.99 1.00 1.03 1.021.04 1.01 1.00 1.03 1.04

With reference to Table 4 and FIG. 6, compared to Example 1, in whichthe weight ratio of the first web (heat-resistant layer)/second web(center layer)/third web (heat-resistant layer) was 1:1:1, the weightratio of Example 2 was 1:1.3:1, and thus, when the weight of the centerlayer was higher than that of the heat-resistant layer, the soundabsorption was low at all frequencies. The weight ratio of Example 3 was1.6:1:1.6, and thus, when the weight of the heat-resistant layer washigher than that of the center layer, the sound absorption was low atall frequencies, compared to Example 1. Meanwhile, in Examples 2 and 3,there was not much difference in sound absorption at all frequencies.Therefore, it was confirmed that when the weight ratio of the compositelayer including the stack of first web (heat-resistant layer)/second web(center layer)/third web (heat-resistant layer) according to the presentdisclosure was close to 1:1:1, the sound absorption was superior.

Test Example 3—Measurement of Sound Absorption Performance Depending onIntrinsic Viscosity (IV) of PET Resin

The composite fiber web of Example 1 and the composite fiber webs ofExamples 4 and 5 were compared for sound absorption. The soundabsorption in Test Example 3 was tested in the same manner as in TestExample 1.

The results of sound absorption testing of Example 1 and Examples 4 and5 are shown in Table 5 below and FIG. 7.

TABLE 5 (FREQ [Hz]) 500 630 800 1k 1.25k 1.6k 2k 2.5k 3.15k 4k 5k 6.3k8k 10k Example 1 0.55 0.72 0.88 0.95 0.98 0.99 1.02 1.08 1.03 1.05 1.051.06 1.04 1.07 Example 4 0.55 0.73 0.87 0.94 0.97 0.99 1.00 1.03 1.021.04 1.01 1.00 1.03 1.04 Example 5 0.53 0.71 0.87 0.93 0.97 0.98 1.001.01 1.02 1.02 1.03 0.97 0.98 1.00

With reference to Table 5 and FIG. 7, as the intrinsic viscosity (IV) ofthe PET resin was lowered to 0.43 upon manufacturing the PET fiber ofthe heat-resistant layer in the composite fiber webs, in which theaverage fiber diameter, weight and thickness were almost the same, soundabsorption became vastly superior. Thus, when the intrinsic viscosity(IV) of the PET resin, which is the material for a PET fiber formanufacturing the heat-resistant layer of the composite fiber web, wasclose to 0.43, it was confirmed that the sound absorption of thecomposite fiber web manufactured using the same was excellent.

Although the preferred embodiments of the present disclosure have beendisclosed for illustrative purposes, those skilled in the art willappreciate that various modifications are possible without departingfrom the scope and spirit of the present disclosure as disclosed in theaccompanying claims, and such modifications should not be understoodseparately from the technical ideas or essential characteristics of thepresent disclosure.

What is claimed is:
 1. A composite fiber web, comprising: a center layercontaining a carbon fiber; and a heat-resistant layer formed on at leastone surface of the center layer.
 2. The composite fiber web of claim 1,further comprising an outer layer formed on the heat-resistant layer andincluding a nonwoven fabric.
 3. The composite fiber web of claim 2,wherein the composite fiber web comprises: 20 to 35 wt % of the centerlayer; 51 to 69 wt % of the heat-resistant layer; and 11 to 14 wt % ofthe outer layer.
 4. The composite fiber web of claim 1, wherein theheat-resistant layer comprises: 43 to 78 wt % of a polyethyleneterephthalate (PET) fiber; and 20 to 55 wt % of a staple fiber.
 5. Thecomposite fiber web of claim 4, wherein the heat-resistant layer furthercomprises 2 to 5 wt % of an antioxidant.
 6. The composite fiber web ofclaim 4, wherein the PET fiber has a fiber diameter of 2 to 12 μm, anintrinsic viscosity (IV) of 0.43 to 0.5, and a melt flow rate (MFR) of150 to 1500 g/10 min.
 7. The composite fiber web of claim 4, wherein thestaple fiber is at least one of a hollow staple fiber, a modifiedcross-section hollow fiber, a modified cross-section fiber, or across-section fiber, and has a thickness of 2.0 to 6.0 denier and alength of 18 to 68 mm.
 8. The composite fiber web of claim 1, having aweight of 580 to 690 g/m², a thickness of 20 to 30 mm, an average fiberdiameter of 2 to 15 μm, a heat-resistant temperature of 225 to 235° C.,a specific surface area of 900 to 2,500 m²/g, and an average noisereduction coefficient (NRC) of 0.92 to 0.94.
 9. A method ofmanufacturing a composite fiber web, the method comprising:manufacturing a center layer containing a carbon fiber; manufacturing aheat-resistant layer; forming a composite layer by stacking theheat-resistant layer on at least one surface of the center layer; andstacking an outer layer on at least one surface of the composite layer.10. The method of claim 9, wherein the manufacturing step of the centerlayer comprises: extruding an isotropic pitch resin; spinning theextruded pitch resin to afford a pitch-based carbon fiber;infusibilizing the carbon fiber; carbonizing the infusibilized carbonfiber; and treating the carbonized carbon fiber with water vapor. 11.The method of claim 10, wherein the spinning step of the extruded pitchresin is performed at a spinning nozzle temperature 50 to 70° C. higherthan a softening temperature of the pitch and at a hot-air temperature30 to 50° C. higher than the softening temperature of the pitch.
 12. Themethod of claim 10, wherein the infusibilizing step of the carbon fiberis performed at a temperature 20 to 30° C. higher than a softeningtemperature of the pitch and at a belt speed of 0.3 to 1 m/min in anoxygen gas atmosphere.
 13. The method of claim 10, wherein thecarbonizing step of the infusibilized carbon fiber is performed at 900to 1100° C. for 30 sec to 5 min in an inert gas atmosphere.
 14. Themethod of claim 9, wherein the manufacturing step of the heat-resistantlayer comprises: crystallizing a polyethylene terephthalate (PET) resin;drying the crystallized PET resin: extruding the dried PET resin;spinning the extruded PET resin to afford a PET fiber; and mixing thePET fiber with a staple fiber.
 15. The method of claim 14, wherein thecrystallizing step of the PET resin is performed at a temperature of 110to 130° C. for 3 to 6 hr to thereby crystallize a surface of the PETresin.
 16. The method of claim 14, wherein the drying step of thecrystallized PET resin is performed at a temperature of 150 to 170° C.for 3 to 4 hr.
 17. The method of claim 14, wherein the spinning step ofthe extruded PET resin is performed at a spinning temperature of 200 to300° C. and a spinning speed of 30 to 120 m/s.
 18. The method of claim14, further comprising heating the PET fiber obtained after spinning theextruded PET resin, wherein the spun PET fiber is heated at a heattreatment temperature of 80 to 120° C. and a belt speed of 0.3 to 1m/min.
 19. The method of claim 9, comprising, on a continuously movingconveyor belt: manufacturing the heat-resistant layer, obtained bymixing a PET fiber resulting from crystallizing, drying, extruding andspinning a PET resin with a staple fiber, into a first web and a thirdweb; manufacturing the center layer, obtained by subjecting apitch-based carbon fiber resulting from spinning an extruded pitch resinto infusibilization, carbonization and water-vapor treatment, into asecond web; and stacking the first web to the third web, which arecontinuously manufactured, in an order of first web/second web/thirdweb.